Was this built with TLDraw SDK?

Maybe I'm missing implementation details, but TLDraw supports nested canvas too.

You can even nest and interact with the current canvas.

Here's the creator demonstrating this.

https://m.youtube.com/watch?v=1C2TdPkj6aQ&t=150

Tldraw's default version of nesting is embedding another full canvas. The benefit would be that the embedded canvas is fully live.

Nestable enables nesting at page management level and encourages deep links to connect things between canvases. This approach has proven to be much more scalable in all of my workflows